Food dehydration method

ABSTRACT

A method for uniformly controlling the amount of medium and moisture residuals in processes for dehydrating particulate comestibles by contact with a heated liquid heat transfer medium within an evacuated drying region wherein each piece of comestible alternately is moved into contact with circulating medium to heat and vaporize its contained-moisture and then removed from such contact substantially into an adjacent vapor space to release a major portion of the vaporized moisture directly into that space and food products having unique structure and composition which are produced by such method.

Ullitfid States Patent 91 Lankford Feb. 27, 1973 FOOD DEHYDRATION METHOD[75] Inventor: Marion P. Lankford, Fremont,

Calif.

[73] Assignee: Vacu-dry [22] Filed: July 1, 1970 [211 App]. No.: 51,535

[52] US. Cl. ..99/204, 34/15, 34/92, 34/109, 34/184, 99/1, 99/100 R,99/100 P,

[51] Int. Cl. ..A23h 7/02, A23b 7/03 [58] Field of Search ...99/199,204, 1, DIG. 5, 100 R, 99/100 P, 246, 403, 410, 411, 412, 413, 414,

[56] References Cited UNITED STATES PATENTS 2,473 ,184 6/1949 Webb..99/204 3,194,670 7/1965 Dorsey et a1. ..99/199 3,239,946 3/1966Forkner ..99/199 X 3,261,694 7/1966 Forkner ..99/199 3,434,410 3/1969Galle ...99/199 X 3,554,038 11/1971 Sweeney et a1. 1 ..34/92 X 150,1274/1874 Bidwell ..34/184 Primary Examiner-S. Leon Bashore AssistantExaminer-Frederick Frei Attorney-Eckhoff and Hoppe [57] ABSTRACT Amethod for uniformly controlling the amount of medium and moistureresiduals in processes for dehydrating particulate comestibles bycontact with a heated liquid heat transfer medium within an evacuateddrying region wherein each piece of comestible alternately is moved intocontact with circulating medium to heat and vaporize itscontained-moisture and then removed from such contact substantially intoan adjacent vapor space to release a major portion of the vaporizedmoisture directly into that space and food products having uniquestructure and composition which are produced by such method.

4 Claims, 8 Drawing Figures FOOD DEIIYDRATION METHOD Several generalizedprocesses for drying comestibles by contacting them with a heated edibleliquid heat transfer medium in a subatmospheric environment have beendisclosed in the patent art including US. Pat. No. 3,194,670 issued July13, 1965 to William R. Dorsey, et al., U.S. Pat. No 3,261,694 issuedJuly 19, 1966 to J. H. Forkner, U.S. Pat. No. 3,239,946 issued Mar. 15,1966 to J. H. Forkner, and US. Pat. No. 2,473,184 issued June 14, 1949to Wells A. Webb. The improvements described herein make practical thosegeneralized disclosures.

One object of this invention is to control the residual medium contentin the final dried product at low levels by manipulation of thecomestible during processing to reduce moisture replacement by themedium.

Another object of the invention is to move the comestible duringprocessing so as to insure uniform dehydration and exposure to thecontacting liquid heat transfer medium while at the same timefacilitating the release of vaporized contained-moisture.

Still another object of this invention is to provide dried comestibleproducts having structures and compositions which are unique andheretofore unattainable by known processing procedures.

An object of the invention also is to provide method and means forminimizing the quantity of heat transfer medium used in processing andconsumed as a residual in the final dried product.

Other objects and advantages of this invention will become apparent froma consideration of the following description and the accompanyingdrawings wherein FIG. 1 is a schematic diagram, partly in perspective,of one system for practicing the drying cycle of this invention;

FIG. 2 is a block flow diagram showing the sequence of the method steps;

FIG. 3 is a schematic diagram of the system of FIG. 1 showing it morecompletely and in more detail;

FIG. 4 is a schematic diagram of one system useful for purifying theliquid heat transfer medium used in the method;

FIG. 5 is an elevational view taken in section on the centerline of thevacuum chamber of FIG. 1;

FIG. 6 is a front elevational view, partly in section, of the vacuumchamber;

FIG. 7 is a perspective view of one form of rotatable basket useful inpracticing the method; and

FIG. 8 illustrates a compartmentalized basket useful in practicing theinvention.

The process, in general, includes development of an evacuated dryingregion maintained at high vacuum levels in the order of about 0.20 to 10millimeters of mercury absolute pressure. A supply of an ediblehydrophobic heat transfer medium which remains liquid at the selectedoperating temperatures and pressures is presented to a portion of or azone within the evacuated drying region. The zone of medium can beeither a bath as is disclosed in the Forkner and Webb patents or ashower such as that described by Dorsey, et al. The remainder of thedrying region is a vapor space in which essentially no liquid heattransfer medium is present. The particular comestible to be processed issupplied either continuously or in batches to the drying region. Duringdehydration each particle is alternately moved into contact with theheated liquid transfer medium to heat and vaporize its containedmoistureand then removed from the medium substantially into the vapor space sothat a major portion of its vaporized contained-moisture is releaseddirectly into the vapor space.

At such time as the desired moisture level is reached the liquid heattransfer medium is withdrawn from the evacuated region and thecomestible centrifuged at gravities in the order of nine times the forceof gravity to remove essentially all medium from the food particlesurfaces. The particles are then cooled, the vacuum released and thedried comestible discharged from the drying region. The entire processcan be performed continuously or on the batch basis which isspecifically described herein.

The comestible may be subjected to a number of preparation steps beforedrying and of variants of the described procedures which depend upon theparticular feed stock and the ultimate product qualities desired. Withreference to FIG. 2 for example, the preparation steps 1 may comprisecooking, roasting, marination, freezing or other preprocessing steps.Typical ones are described in connection with the examples which follow.The particulate comestible is then 2 sealed in a vacuum chamber, and 3vacuum is drawn on the chamber. Liquid heat transfer medium is heated 4and supplied to the chamber to contact the comestible under themanipulative conditions described above. The medium preferably isrecycled 6 and continuously or intermittently purified 7 to removecontaminants resulting from contact with the comestible or otherwise.Moisture from the chamber is removed 8 either as condensate through atrap or as vapor through the vacuum system or both. At a selectedmoisture level medium is withdrawn from the chamber and the comestiblespun or centrifuged 9 to remove any remaining medium from the foodsurfaces while still under vacuum. The comestible is then cooled 10, thevacuum released 11, and the dry product unloaded 12 from the vacuumchamber.

The liquid heat transfer medium has been handled in the system andapparatus described schematically in FIG. 1 which is useful forpracticing the invention on a batch basis. It includes a vacuum chamber20 and means, not illustrated, for drawing vacuum within the chamber at21. The vacuum means can be a positive displacement pump, oil diffusionpump or steam jet ejectors all of which are commercially available todevelop the vacuum levels contemplated herein. Within vacuum chamber 20is basin 22 which confines the liquid heat transfer medium so that, ifdesired, it may be applied to the comestible as a bath. Within basin 22is a generally cylindrical foraminous basket 23 rotated or rocked upondrive shaft 24 by a variable speed motor drive assembly 25 mountedexterior to and on the vacuum chamber wall. The basketconfines the foodparticles but is perforated substantially over its entire surface sothat water vapor can freely move out of it and liquid heat transfermedium can move in. The interior of basin 22 through a plurality ofperforations 26 communicates with the atmosphere of vacuum chamber 20 sothat water vapor can freely pass from the basin to the vacuum system andthe interior of basket is under vacuum. Liquid heat transfer mediumthrough distributor 27 during the drying phase of the describedembodiment supplies a continuous flow of medium that falls by gravityover the particulate comestible 28 contained within the basket 23.

The heat transfer medium is withdrawn by pump 29 throughout outletconduit 30 that drains the basin 22. The pump 29 circulates mediumthrough heater 31 and back into the vacuum chamber 20 via inlet conduit32 to the distributor 27. Heater 31 adds sufficient heat to the mediumto make up the heat lost through moisture vaporization in basin 22.Depending upon the particular food being processed, a level of mediumcan be maintained in the basin 22 to develop a zone of medi um which isa bath 33. Its contact with the food under process is accomplished byimmersion of the latter in the bath. Alternatively, no liquid level iscarried in basin 22 for many applications and in such cases contact ofmedium with the food being processed is entirely by shower fromdistributor 27. In either alternative the movement of comestibleparticles also prevents their clumping as frequently occurs in prior artmethods.

The medium circulation system of FIG. 1 also includes purifying themedium as is shown more particularly in FIG. 4. Purification includescontinuously or intermittently mixing all or a portion of thecirculating medium at mixer 34 with an emulsifiable flushing liquid orsolvent for the impurities in the medium; heating the mixed phases toassist extraction from the medium by the flushing liquid; and thenseparating, as at 35, the cleansed medium from the flushing liquid orsolvent which now carries the impurities of the untreated medium anddelivers them to further separation means or to the waste disposal drainas illustrated.

During exposure of the processed food to the liquid heat transfermedium, the foraminous basket 23 rotates at a low speed in the order of50 rpm. In those instances where a liquid level is maintained in basin22 this rotation of the basket periodically immerses the food particlesunder process in the bath and subsequently carries each particlesubstantially out of the bath into the vapor space lying above it. Theremost of the contained-moisture vaporized by the heated medium isreleased directly into the vapor space through, at most, a thin residualfilm of medium carried on the food particle surfaces. Since eachparticle periodically moves substantially out of the bath or at least toits surface, it never is exposed for any length of time to a head ofliquid medium overlying it with the consequent undesirable hydrostaticpressure that otherwise partially nullifies the effect of the vacuum inthe chamber, inhibits moisture release from the particles and/or drivesmedium into the voids remaining in the food particles after suchmoisture release.

In instances where heat transfer is entirely through a shower of medium,rotation of the basket again at low speeds in the order of 10 50 rpmtumbles the food being processed in the basket and uniformly exposeseach particle to the descending shower. This eliminates the umbrellaeffect of the top layers of comestible in a static system which tend toshield lower layers from the medium shower and results in nonuniformexposure to the medium.

FIGS. 3 8 illustrate in more detail one system and the equipment usefulfor practicing the method on a batch basis. The vacuum chamber as shownon FIGS. 5 and 6 is a rigid steel cabinet 40 provided with a gasketedand windowed access door 41. The chamber carries within it basin 22which is another steel cabinet with its top pierced by multipleperforations 26 so that the evacuated atmosphere within vacuum chamber20 also persists within basin 22 and basket 23 and removed water vaporcan pass to the vacuum system with minimum entrainment of medium. Thebasin 22 also has a gasketed access door 42 with a window so thatoperations within can be viewed from outside the vacuum chamber. In thedescribed embodiment the basin 22 has two pairs of wheels 43 supportedupon tracks 44 so that the basin can be rolled in and out of the vacuumchamber. Outlet conduit 30 from the bottom of basin 22 is a flexiblecoupling that communicates the basin through the vacuum chamber wall tothe medium circulating system.

The described medium circulating system includes positive displacementpump 29 which draws medium from the basin 22 through the outlet conduit30. The outlet line 49 is provided with block valve 50 and a venturitype ejector 51, having its throat connected to the outlet line, assiststhe pump draw medium from the basin. The ejector 51 is driven by highpressure medium in recirculating line 52 from the discharge of pump 29and is controlled by throttle valve 53. The circulating pump 29 movesmedium through flow indicator S4 and a pair of filters 55, then throughflow meter 56 and the tube side of heat exchanger 57. In the embodimentdescribed steam on the shell side of the exchanger 57 heats the mediumto its operating temperature. That temperature is controlled bytemperature controller 58 which regulates steam flow by actuating valve59. From heat exchanger 57 the heated medium flows directly to thevacuum chamber 20 through inlet conduit 32 and distributor 27 during thedrying portion of the cycle. Alternatively, all or a portion of themedium can be diverted by valve 60 to the purification system shown onFIG. 4 or to storage reservoir 61 through solenoid valve 62. Reliefvalve 63 on the pump discharge provides pressure relief to the samereservoir 61 and medium make-up is achieved through make-up line 64.

Inlet conduit 32 also flexibly interconnects the medium return line atthe vacuum chamber top with the distributor 27 mounted within basin 22.This distributor can be simply a pipe with plural perforations along itslength or it can be fitted with nozzles, in both ways, for uniformdistribution of medium over foraminous basket 23.

The described basket is cylindrical in shape with a foraminous shellsecured between a pair of hubs 71 on drive shaft 24. A foraminous door72 in the shell providesmeans for loading and unloading the basket withfood to be processed. The basket perforations are small enough topreclude passage of the food particles through them under moderate andhigh speeds of rotation.

FIG. 8 illustrates another form of basket which is compartmentalized tosegregate the processed food. It comprises a shell 70' fabricated fromlarge mesh screening material and has a plurality of radially disposeddividers 73 of the same material which divide its interior intosegments. The far side of the basket is also screening material andretainer 74 is located on the near side of the basket and holds largepiece foods 28, such as pork loins, in the basket. This design is usefulin processing foods which initially are frozen, such as meat and fish,that otherwise tend to refreeze together and agglomerate if notinitially separated one piece from the other.

Also in the embodiment described, vacuum is drawn on the vacuum chamber20 by a positive displacement pump 80 at vacuum connection 21. Watervapor is first removed as much as possible by condensation from the airand vapor being drawn to vacuum pump 80 by cooling coil 81 supplied withrefrigerant as at 82. The condensed moisture is caught in catch basin 83and conducted out of the vacuum chamber through trap means referred togenerally as 84.

The improved processing steps are applicable to sub stantially allparticulate foods and especially to a variety of cellular comestiblesincluding meat, poultry, fish, nuts, vegetables and fruits. Thefollowing examples are typical;

EXAMPLE 1 A unique puffed apple confection is produced by the processfrom fresh apple wedges. Fresh apple, approximately one-half inch,wedges are first treated as is customary by a 60 second dip in a 1percent sodium bisulfite solution to prevent browning. Fresh applemoisture content is about 85 percent by weight on a dry basis and thefresh wedges contain about 14 percent sugar.

The apples are prepared for processing into the unique structure byfirst marinating them by immersion for 1 hour in a 50 percent aqueoussugar solution at atmospheric pressure. The sugarsolution in an openkettle is held at temperatures within the range of 100 to 190 F.,preferably about 180 F. The solution is 50 percent water and 50 percentsugar comprising about two-thirds corn syrup solids and one-thirdsucrose. Seasonings such as malic acid, citric acid, cinnamon andflavorings as well as sodium bisulfite preferably are added in smallamounts.

The marinated wedges are then drained and closed into the foraminousbasket 23 of the type illustrated in FIG. 7. The doors 42, 41 in basin22 and vacuum chamber 20, respectively, are then sealed and vacuum drawnon the vacuum chamber to a level of about millimeters of mercuryabsolute pressure. Heated liquid medium, for example a mixed cotton andsoybean oil sold under the tradename Durkex 500, then is circulatedthrough the basin at temperatures in the range of 190 to 200 F. A liquidlevel in the basin 22 is allowed to build up to about the centerline ofthe basket. The basket rotates slowly at about rpm. The medium iscirculated through the system in a ratio of about 100 to l with respectto the apple wedge load in the basket. The wedges are processed underthese conditions for about 1 hour at which time their moisture contentreduces to about 3 8 percent.

Then, the medium is drained from the basin 22 and the basket is rotatedrapidly at about 360 rpm under the same vacuum conditions for l to 2minutes. With a basket diameter of 18 inches this results in acentrifugal force at the basket periphery of about nine times the forceof gravity. Centrifugation removes undrained medium from the surfaces ofthe apple wedges as well as medium which may have permeated the applematerial but is not tightly bound therein by capillary action.

Following centrifugation the chamber pressure is rapidly drawn downlower to a level of about 1.0 to 0.20 millimeters of mercury absolute.The moisture level consequently drops to 2% percent or less. Itsevolution evaporatively cools the apple wedges over a period of 60minutes to about F. The wedges can be observed to puff substantiallyduring this evaporative cooling step. The vacuum then is broken byadmission of nitrogen gas and the now dried apple wedges are unloadedfrom the chamber.

The wedges have a final moisture content of about 2% percent by weightand have a medium residual of about 3 to 10 percent. The wedge structureis unique. It comprises a honey-comb structure comprising a singlecavity substantially triangular in cross-section or a plurality ofsmaller irregular cavities formed in the center of the three wedge wallswhich are very friable and have an expanded cell structure. The overallwedge appearance is slightly puffed with the sidewalls of the wedgeconcaved outwardly from their original fresh configuration.

EXAMPLE 2 Lean pork loins at about 60 percent moisture are first quickfrozen with nitrogen at least to a temperature level of 20 F. The frozenpork is loaded into a foraminous basket of the type illustrated in FIG.8 wherein each piece is segregated from the other in a separatecompartment. After sealing the basin and vacuum chamber, vacuum is drawnupon the chamber to a level of about 1,500 to 500 microns. Medium suchas the mixed vegetable oils of Example 1 circulates through the basin attemperatures ranging from 90 to 150 F., preferably about F. Inprocessing pork it has been found preferable not to maintain a level ofheat transfer medium in the basin 22. Heat transfer is done entirely bya shower of heated medium over the pork emerging from distributor 27.The basket rotates slowly at about 20 rpm.

After about 3 1% hours of processing under these conditions the moisturelevel is less than 2 percent. The medium is drained from the basin andthe basket rotated again for l to 2 minutes under the same vacuumconditions at about 360 rpm or a speed sufficient to attain centrifugalforces about nine times that of gravity at the basket periphery. Thepork is then allowed to cool, the vacuum broken by admission of liquidnitrogen and the dried pork loins removed from the chamber.

The final product has a quality and structure similar to that offreeze-dried material with a residual moisture content of less than 2percent and a residual medium content in the range of 37 to 38 percent.Total drying time is substantially less than the time required to reachthe same moisture level by freeze-dry techniques.

EXAMPLE 3 Low fat potato chips can be made by the described processeshaving a residual fat content in the order of half that of commerciallyavailable potato chips produced by deep fat frying.

Raw Russett potato slices about 0.050 inches in thickness initially areloaded into the basket of FIG. 7

and precooked in liquid medium for about 1 3 minutes under atmosphericpressure at about 225 to 250 F. The precook provides the flavor andbrowning usually expected in commercial potato chips. During the precookthe liquid medium temperature is allowed to drop to the range of 180 to200 F.

The vacuum chamber is then sealed and a vacuum drawn to about 1millimeter of mercury absolute pressure. The liquid heat transfer mediumagain is the mixed vegetable oils of Example 1 circulated attemperatures in the range of 180 to 225 F., preferably at the upper endof that range. The medium level in basin 22 is at about the basketcenterline. The potato slices are processed under these conditions for aperiod of about 30 to 40 minutes with the basket rotated at about 20rpm.

The medium then is withdrawn from the basin and the potato slicescentrifuged for one to two minutes under the same vacuum conditions atabout 360 rpm or a speed sufficient to develop centrifugal forces ofabout nine times the force of gravity at the basket periphery.

The vacuum is broken with nitrogen and the now dried chips unloaded fromthe chamber. They have a residual moisture content of about 0.5 percentby weight and residual medium in the range of to 18 percent comparedwith the typical 35 percent fat content for commercially available deepfat-fried potato chips.

EXAMPLE 4 Fresh or frozen green beans such as California Bush varietiesare cut to suit need and dipped in about a 1 percent magnesium or sodiumbisulfite solution for color preservation. The beans have an approximate90 percent moisture content.

The beans are placed into a foraminous basket 23 of the type illustratedin FIG. 7 and vacuum on the chamber is drawn down to a level of about 10millimeters of mercury absolute pressure. At that level heated medium,for example, the mixed cotton and soybean oil described in Example 1, isstarted through the basin at temperatures in the range of 170 190 F. Aliquid level in the basin 22 is allowed to build up to about the centerline of the basket and the chamber pressure is drawn down to a level inthe order of one-half millimeter of mercury absolute pressure. Thebasket rotates slowly at about rpm. The beans are processed under theseconditions for about 45 60 minutes at which time their moisture contentreduces to about 3 percent.

The medium then is drained from the basin 22 and the basket is rotatedrapidly for l 2 minutes under the same vacuum conditions at about 360rpm or a speed sufficient to develop centrifugal forces at about ninetimes the force of gravity at the basket periphery.

Next the beans are cooled and the vacuum broken with nitrogen. They havea residual moisture content of 2 b to 6 percent on a dry weight basisand residual medium in the range of 8 to 16 percent. The beans retaintheir original size, shape and color without shriveling of the softtissue surrounding the seed cell.

The circulating liquid heat transfer medium progressively picks upsoluble contaminants from the comestibles being processed. Thesecontaminants either must be removed from the medium or a continuousmakeup of fresh medium used to hold them to tolerable levels.

For instance, in processing the apple wedges of Example 1 the mediumbecomes contaminated by the water soluble marination sugar and solublesolids in the apples themselves as it continuously washes through them.These contaminants eventually cause off-color and off-taste product ifnot removed.

It has been found that a purification system as described in FIG. 4 isuseful to remove these contaminants by mixing the heat transfer mediumwith an emulsifiable flushing fluid or solvent for the contaminantswhich extracts the contaminants from it and after separation from themedium carries the impurities off in solution for disposal orreclamation procedures. For the apple wedges of Example 1, for instance,medium either continuously or intermittently is directed through thepurification system by opening control valve 100. Contaminated mediumflows through sight glass 101 where its turbidity, etc. can be observed,indicating flow meter 102, flow regulator 103, and check valve 104 to avariable speed motor driven mixer 105 which emulsifies the medium andsolvent. A suitable unit is a multiple propeller type mixer withintermediate baffles such as is shown schematically in FIG. 4.

Since the impurities for the apple example described above principallyare water soluble sugars, hot water or a mixture of water and steam atabout 150 F. through temperature control valve 106, another indicatingflow meter 107, flow regulator 108 and check valve 109 is also suppliedto the mixer 105. The hot water and transfer medium are thoroughly mixedin ratios ranging from 25 percent water percent medium to 75 percentwater 25 percent medium. The outflow from the mixer is an oil wateremulsion. It is steam heated in exchanger 110 to about F. to enhancesolution of contaminants in the solvent and then passed through anothersight glass 111, by which its emulsification can be observed, tocentrifuge 112. Centrifugation there breaks the emulsion and separatesthe oil and water phases. The water phase and the soluble contaminantsdissolved in it flow through effluent sight glass 113 to waste disposalor to reclamation processing. The medium or oil phase passes through aclarified medium sight glass 114 and then returns to the mediumcirculating system as at 115. Samples of clarified medium may be takenat sample connection 116 to determine its suitability for recycle.

The foregoing systems and equipment have been described for clarity ofunderstanding only and no unnecessary limitations should be understoodfrom them for modification will be apparent to those skilled in thisart. The invention is defined by the appended claims.

I claim:

1. In a process for removing moisture from a comestible by contacting itwith a heated edible liquid heat transfer medium within an evacuateddrying region, the improvement comprising the steps of maintaining azone of medium in said drying region;

simultaneously defining a vapor space within said drying region separatefrom said zone of medium; continuously and alternately, first moving thecomestible into contact with the medium in said zone to vaporize itscontained-moisture; and

then removing said comestible from said zone substantially into saidvapor space to release a major portion of the vaporizedcontained-moisture directly into said vapor space.

2. The process of claim 1, including the additional steps ofcentrifuging the liquid heat transfer medium from the surfaces of saidcomestible within said drying zone at a predetermined moisture content;

cooling said comestible;

increasing the pressure in said drying zone to atmospheric;

and then removing the comestible from said drying zone.

3. In a process for removing moisture from a comestible by contacting itwith a heated edible liquid heat transfer medium within an evacuateddrying region, the improvement comprising the steps of maintaining abath of medium in said drying region;

simultaneously defining a vapor space within said drying region separatefrom and overlying said bath of medium;

continuously and alternately, first moving the comestible into contactwith the medium in said bath to vaporize its contained-moisture; and

then moving said comestible at least to the surface of said bathadjacent to said vapor space to release a major portion of the vaporizedcontained-moisture substantially into said vapor space.

4. The process of claim 3, including the additional steps ofcentrifuging the liquid heat transfer medium from the surfaces of saidcomestible within said drying zone at a predetermined moisture content;

cooling said comestible;

increasing the pressure in said drying zone to atmospheric;

and then removing the comestible from said drying zone.

2. The process of claim 1, including the additional steps ofcentrifuging the liquid heat transfer medium from the surfaces of saidcomestible within said drying zone at a predetermined moisture content;cooling said comestible; increasing the pressure in said drying zone toatmospheric; and then removing the comestible from said drying zone. 3.In a process for removing moisture from a comestible by contacting itwith a heated edible liquid heat transfer medium within an evacuateddrying region, the improvement comprising the steps of maintaining abath of medium in said drying region; simultaneously defining a vaporspace within said drying region separate from and overlying said bath ofmedium; continuously and alternately, first moving the comestible intocontact with the medium in said bath to vaporize its contained-moisture;and then moving said comestible at least to the surface of said bathadjacent to said vapor space to release a major portion of the vaporizedcontained-moisture substantially into said vapor space.
 4. The processof claim 3, including the additional steps of centrifuging the liquidheat transfer medium from the surfaces of said comestible within saiddrying zone at a predetermined moisture content; cooling saidcomestible; increasing the pressure in said drying zone to atmospheric;and then removing the comestible from said drying zone.